1. Field of the Invention
The present invention relates generally to optical technology, and more particularly, to optical input devices.
2. Description of the Related Arts
Optical technology is used in many contexts, including optical input devices, such as a mouse. In most of these devices the optical system conventionally has a sensor for determining the displacement of the optical device relative to a surface. For example, in the case of an optical mouse, the mouse has at least one optical sensor to determine the movement of the mouse on a surface, such as a desktop or mouse pad. The movement of the mouse on the surface translates to movement of a mouse pointer or cursor on a display associated with a host.
The movement or displacement of an optical mouse is determined by comparing two different images captured at two different moments in time and possibly two different locations on the surface. The ability of an optical mouse to track is highly dependent on the quality of the images. If the images are good quality, the optical mouse can more easily track.
Sensors used in conventional optical mice can track on surfaces which are capable of diffusing light, such as paper, wood, paint, metal, and the like. This is because conventional imaging is based on using the optically rough nature of regular surfaces (e.g., wood, cloth, etc.). Thus, problems arise with imaging when the surface is made of optically smooth materials which do not diffuse a sufficient amount of light, such as a surface made of glass or other transparent material. An example of this is a glass table. In addition, problems also arise when a layer of glass or other transparent material is positioned on top of a diffusing surface. An example of this is a glass sheet placed on top of a wooden desk. Let us consider each of these situations separately.
When a surface made of a transparent material such as glass is to be used as a tracking surface, sufficient light is not diffused by the surface to make conventional tracking possible.
When a layer of glass or other transparent material is placed on top of a diffusing surface, such a configuration causes a change in the distance (referred to as the “z distance”) between the optical sensor and the imaging surface, i.e., the diffusing surface beneath the transparent layer. Hence, conventional methods of illumination and imaging may result in improper focus, inadequate illumination, and/or spot shift or poor overlap of the illuminated spot and the imaged area. These problems can prevent the sensor from accurately tracking displacement (mouse motion).
Attempts to address some of these issues in conventional systems result in other short-comings. For example, a problem arises with accurate detection of lifts. In particular, when a user lifts the mouse, e.g., intending to reposition it on the tracking surface without moving the cursor on the screen, the cursor on the screen follows the movements of the mouse throughout the lift when, in fact, it should not do so.
Moreover, problems discussed above are not limited to optical input devices. Similar problems exist for other devices that use optical technology to capture images and determine location and movement. An example of another device that may experience such shortcomings is a handheld scanner.
Accordingly it is desirable to provide an optical device that can accurately track displacement relative to a surface, even when a layer of transparent material is placed between the optical device and the tracking surface or when the user desires to track only on a transparent material, as well as to provide accurate lift detection.